Optical apparatus and laser display apparatus having laser beam scanner each

ABSTRACT

An optical apparatus is disclosed which has a scanner for scanning a predetermined area with a laser beam. The optical apparatus comprises: a laser source; a scanner having a scanning mirror for causing a laser beam generated by the laser source to scan; an angle sensor for sensing angles of the scanning mirror of the scanner; a fault detection block for determining whether the scanning mirror operates safely and normally based at least on angle information coming from the angle sensor; and a projection control block for controlling projection of the laser beam based on fault detection information coming from the fault detection block.

BACKGROUND OF THE INVENTION

The present invention relates to an optical apparatus and a laserdisplay apparatus each having a laser beam scanner.

Today, devices and apparatuses handling laser beams are required tocomply with rigorous safety standards. The equipment utilizing laserbeams includes light show devices and bar code readers used by POS(point of sale) systems. Each of these devices is furnishedillustratively with a scanner for scanning a target area with a laserbeam.

Another typical laser beam device is a display apparatus as part oftheater-use projection equipment for projecting images to be viewed by alarge audience. In order to acquire a brightly projected image on alarge screen, the display apparatus first forms a one-dimensionaloptical image using one-dimensional light modulators and then causes theoptical image thus formed to be scanned perpendicularly for projection,whereby a two-dimensional optical image is projected.

Where the one-dimensional optical image is scanned so as to acquire thetwo-dimensional projected image, a high-powered laser beam is directedat the screen. Because this laser beam is emitted externally, it issubject to strict safety standards.

In display apparatuses such as scanner-equipped projectors, the scannercould be stopped for some reason. In such a case, the dose of the laserbeam per unit projected area could largely exceed normal levels, posinga threat to safety.

Laser scanner-equipped projection display apparatuses designed forhigher safety have been proposed. One such apparatus is disclosedillustratively in Japanese Patent Laid-open No. 2000-194302 (as claimedin claim 3 and described in particular in Paragraph p. 20, 1.24 to p.21, 1.15).

The projection display apparatus proposed by the above-cited patentapplication detects the scan timing of the scanner during operation. Ifthe detected timing is found to deviate from reference timing, scanningwith the laser beam is stopped. It should be noted that the preferredscanning means for the proposed apparatus is a polygon scanner thatrotates at a constant velocity.

There also exist optical and display apparatuses which utilizegalvanometer scanners. Unlike polygon mirrors rotating at a constantspeed in a fixed direction, the galvanometer scanner makes a reciprocalrotary motion that has a predetermined amplitude, a constant cycle, anda fixed rotation pattern but not a steady speed.

The present invention has been made in view of the above circumstancesand provides a laser display apparatus having a scanning safeguardsystem. This system stops laser beam emission upon detection of ascanner being stopped abnormally for whatever reason, so that the doseof the laser beam will not exceed safety standards. The inventivesafeguard system works not only with the polygon mirror setup where thescanner (i.e., mirror) rotates at a constant speed, but also with thegalvanometer mirror arrangement in which the mirror moves inreciprocating motion for scan.

SUMMARY OF THE INVENTION

In carrying out the invention and according to a first aspect thereof,there is provided an optical apparatus having a scanner for scanning apredetermined area with a laser beam, the optical apparatus comprising:a laser source; the scanner having a scanning mirror for causing a laserbeam generated by the laser source to scan; an angle sensor for sensingangles of the scanning mirror of the scanner; a fault detection blockfor determining whether the scanning mirror operates safely and normallybased at least on angle information coming from the angle sensor; and aprojection control block for controlling projection of the laser beambased on fault detection information coming from the fault detectionblock.

Preferably, the optical apparatus according to the first aspect of theinvention may further comprise a diagnosis function for determining uponpower-up whether the angle sensor, the fault detection block, and theprojection control block function normally.

With the above-outlined optical apparatus in operation, the faultdetection block may detect a scanner system failure based on theinformation sensed by the angle sensor. In that case, the projectioncontrol block controls laser beam emission so that the dose of the laserbeam emitted externally will not exceed the dose level stipulated forthe laser class to which the apparatus belongs.

The inventive optical apparatus monitors scanning safeguard status byuse of a detection sensor verifying that the projection control blockoperates normally. The apparatus also uses a motor driver to detect afaulty state in an overall control block and a motor driver blockimplementing the diagnosis function, whereby a reliable safeguardfeature is realized.

According to a second aspect of the invention, there is provided a laserdisplay apparatus having a scanner for scanning a predetermined areawith a laser beam, the laser display apparatus comprising: a lasersource; a light modulator for modulating a laser beam generated by thelaser source; the scanner having a scanning mirror for causing the laserbeam modulated by the light modulator to scan; an angle sensor forsensing angles of the scanning mirror of the scanner; a fault detectionblock for determining whether the scanning mirror operates safely andnormally based at least on angle information coming from the anglesensor; and a projection control block for controlling projection of thelaser beam based on fault detection information coming from the faultdetection block.

Preferably, the laser display apparatus according to the second aspectof the invention may further comprise a diagnosis function fordetermining upon power-up whether the angle sensor, the fault detectionblock, and the projection control block function normally.

With the above-outlined laser display apparatus in operation, the faultdetection block may detect a scanner system failure based on theinformation sensed by the angle sensor. In that case, the projectioncontrol block controls laser beam emission so that the dose of the laserbeam emitted externally will not exceed the dose level stipulated forthe laser class to which the apparatus belongs.

The inventive laser display apparatus monitors scanning safeguard statusby use of a detection sensor verifying that the projection control blockoperates normally. The apparatus also uses a motor driver to detect afaulty state in an overall control block and a motor driver blockimplementing the diagnosis function, whereby a reliable safeguardfeature is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of this invention will become apparentupon a reading of the following description and appended drawings inwhich:

FIG. 1 is a schematic block diagram of a laser display apparatusaccording to the invention;

FIG. 2 is a schematic perspective view indicating key parts of a lightmodulator for use by the laser display apparatus;

FIG. 3 is an explanatory view showing how the light modulator works;

FIG. 4 is a schematic block diagram of a scanning safeguard system foruse by an optical apparatus according to the invention;

FIGS. 5A and 5B are schematic views showing how the presence or absenceof laser beam emission is detected and how the dose of the emission iscontrolled;

FIGS. 6A and 6B are waveform charts representative of mirror rotationangles and mirror rotational speeds in effect during normal scanneroperation;

FIG. 7 is a graphic representation of an instruction signal waveformsent to a motor driver, a rotational angle detection signal waveformderived from a mirror, a supply current waveform from a motor, and amirror speed waveform from the mirror, all waveforms being used fordetecting a scanner speed fault;

FIGS. 8A and 8B are waveform charts comparing the normal state of themirror with its stopped state in terms of mirror angles and mirrorspeeds;

FIG. 9 is a schematic block diagram of a fault detection block fordetecting a mirror speed fault;

FIGS. 10A and 10B are waveform charts plotting angle information outputby the scanning mirror and depicting a signal waveform representative ofthe output angle information with regard to predetermined thresholdlevels Hth1, Hth2, Lth1, and Lth2;

FIG. 11 is a schematic block diagram of a fault detection block fordetecting a cycle fault and an amplitude fault;

FIGS. 12A and 12B are schematic explanatory views illustrating how acomparison block compares reference data and threshold levels obtainedfrom a memory with angle information, i.e., measured data;

FIGS. 13A and 13B are schematic explanatory views showing how thecomparison block compares reference data and threshold levels obtainedfrom a memory with angle information, i.e., measured data, in terms ofthreshold level settings and fault detection timings;

FIG. 14 is a schematic block diagram outlining how each fault detectionblock acquires reference data and threshold levels and how comparisonblocks compare the acquired data with measured data;

FIG. 15 is a schematic block diagram showing how each fault detectionblock acquires reference data and threshold levels in a first embodimentof the invention;

FIG. 16 is a schematic block diagram showing how each fault detectionblock acquires reference data and threshold levels in a secondembodiment of the invention;

FIG. 17 is a schematic block diagram of a determination signalacquisition block which acquires a determination signal based on theoutput from fault detection blocks detecting faults by sensing speeds,cycles and amplitudes; and

FIG. 18 is a flowchart of steps executed by a scanning safeguard systemaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Described below with reference to the schematic block diagram of FIG. 1is a projection apparatus accommodating an optical apparatus 16 and alaser display apparatus 14 each equipped with a laser beam scanneraccording to the invention. The setup of FIG. 1 includes: laser sources1R, 1G and 1B generating laser beams of red, green and bluerespectively; condensing lenses 3 furnished in combination with thelaser sources; and light modulators 4R, 4G and 4B composed of GLV(grating light valve) each and used to obtain a one-dimensionalprojected optical image.

Optical images modulated by the light modulators 4R, 4G and 4B inkeeping with a projected optical image are merged by dichroic mirrors 5and 6. The merged image reaches a scanner 8 through a projection lens 7.With its reflected light, the scanner 8 scans a screen 9.

The light modulators 4R, 4G and 4B are typically constituted either by ablazed type optical diffraction grating or by GLV made of a micro ribbonoptical diffraction grating. As shown in FIG. 2, the GLV makeupcomprises a plurality of pixels 11 (e.g., 1,088 units) arrangedone-dimensionally, each pixel being formed illustratively by adiffraction grating made up of six parallelly arranged micro ribbons 10.

In each pixel 11, a counter electrode 13 is positioned on a substrate 12under the micro ribbons 10 in a manner having a predetermined clearancefrom, and commonly opposed to, the micro ribbons 10. Illustratively, apredetermined voltage is applied between every other micro ribbon 10 andthe counter electrode 13. The voltage application causes the middleportion of each voltage-affected ribbon 10 to move into a predetermineddistance relative to the substrate 10 and stay there. As shownschematically in FIG. 3, incident light Li entering the micro ribbons 10of each pixel, i.e., a beam coming from one of the laser sources 1R, 1Gand 1B, produces primary diffracted light beams Lr(+1) and Lr(−1). Inthis manner, the light from each of the laser sources 1R, 1G and 1B ismodulated by the GLV-based light modulators 4 into positive and negativeprimary diffracted light whose presence or absence or whose degrees inintensity are controlled as needed.

A one-dimensional optical image produced by the light modulators 4R, 4Gand 4B through modulation and merging is scanned by the scanner 8perpendicularly to a one-dimensional direction (e.g., scannedhorizontally) on the screen 9. The scan generates a two-dimensionaloptical image that is projected onto the screen 9.

In FIG. 1, reference numeral 2 stands for mirrors that cause laser beamsfrom the laser sources 1G and 1B to pass through the condensing lenses 3before entering the light modulators 4G and 4B respectively. In theabove-mentioned setup where horizontal scanning is effected, the scanner8 is formed illustratively by a scanning mirror such as a galvanometermirror rotating reciprocally. around a perpendicular axis.

Described below with reference to the schematic block diagram of FIG. 4is a scanning safeguard system 15 that controls the inventive opticalapparatus having a laser beam scanner to comply with safety standards.The scanning safeguard system 15 includes: an angle sensor 21 forsensing mirror angles of the scanner 8; a fault detection block 22 fordetermining whether the scanning mirror operates normally and safely; aprojection control block 23 for controlling the externally directedlaser beam emission; a detection sensor 24 for detecting signals outputby the projection control block 23; an overall control block 25 forsupplying illustratively a shield control signal to the projectioncontrol block 23; a motor driver 27 receiving signals from the overallcontrol block 25; and a scanner motor 26 for rotating the scanningmirror of the scanner 8 under instructions from the motor driver 27.

The angle sensor 21 is attached illustratively to the scanner motor 26rotating the scanner. In operation, the angle sensor 21 senses rotationangles of the motor in order to determine the angle of scanner mirrorrotation, and forwards a detection signal reflecting the detected angleto the fault detection block 22.

The angle sensor 21 is formed illustratively by a capacitance-operatedangle sensor attached to the scanner motor 26. However, the angle sensoris not limited to the capacitance type. The sensor may be of any one ofdiverse types including an encoder sensor, an optical position sensor, asensor for sensing the rotating shaft of a motor or a mirror, and amirror surface sensor.

The projection control block 23 receives the shield control signalprimarily from the overall control block 25 so as to control thepresence or absence of the laser beam or its dose during laser beamprojection. Illustratively, the projection control block 23 modifies thelaser beam path by controlling the scanner mirror, and shields theprojected light using mechanical shutters. Furthermore, the projectioncontrol block 23 controls modulation levels of the light modulators 4R,4G and 4B (FIG. 1); stops laser oscillation; or stops the supply ofcurrents to laser diodes (LD).

The controls above may also be effected using mirrors and an integratingsphere as shown in FIGS. 5A and 5B. Normally, as depicted in FIG. 5A, aplurality of mirrors 18 are located in such relations to one anotherthat they will not shield the laser beam projection. Upon receipt of ashield control signal indicative of a detected fault, the mirrors 18 aremoved into such relations to one another that the laser beam projectionis shut down and the laser beam is guided to the integrating sphere. Theaction not only shields the laser beam (projected light) but alsoverifies deactivation of the beam emission through measurement with theintegrating sphere.

The detection sensor 24 checks primarily to see whether the projectioncontrol block 23 functions normally. This is a sensor designed mainly toascertain the workings of the projection control block 23. When theprojection control signal is compared with the result of detection bythe detection sensor 24, the projection control block 23 can bemonitored for any faulty operation. The sensing of the detection sensor24 is brought about illustratively by measuring the dose of theprojected laser beam or by observing positional relations between themoving components involved.

The overall control block 25 exercises overall control on the inventiveoptical apparatus and the inventive laser display apparatusincorporating the optical apparatus. Illustratively, the overall controlblock 25 receives various kinds of signal information such asinstruction signal information and drive current information from thefault detection block 22, and uses the received information as a basisfor giving an instruction signal or an enable signal to the motor drive27 as needed. In turn, the motor driver 27 issues operation instructionsto the scanner motor 26 for mirror control purposes.

The overall control block 25 further uses the diverse kinds of signalinformation such as instruction signal information and drive currentinformation from the fault detection block 22 as well as an error flagfrom the motor driver 27 as a basis for controlling the projectioncontrol block 23. That is, the projection control block 25 is instructedto turn on and off laser beam projection and to control the beamemission in keeping with a predetermined sequence.

The overall control block 25 also outputs to the fault detection block22 a mode signal indicative of operation mode. This signal is used bythe fault detection block 22 for comparison with the enable signal.Furthermore, the overall control block 25 monitors key components forstatus in terms of projection conditions such as projection frequency,duty ratio, zoom ratio, and laser power level.

As described, the overall control block 25 not only sends signals to theinventive optical apparatus or laser display apparatus (e.g., projector)but also prompts the components involved to work in smooth collaborationwith one another so that the scanning safeguard system will function ina steady and efficient manner. Where necessary, the overall controlblock 25 monitors the entire system and thus functions as part of asystem-wide diagnosis facility.

The scanning safeguard system also acts to inhibit laser beam projectionif the overall control block 22 becomes faulty. This is accomplishedbecause the fault detection block 22 is independently on the lookout forfault and prompts the projection control block 23 to act in case ofabnormality.

Given an instruction signal from the overall control block 25, the motordriver 27 issues an operation command to the scanner motor 26 for motoroperation control. Feedback control is implemented when the motor driver27 is supplied with information about the actual angle attained by thescanner motor 26, the information coming from the angle sensor 21attached to the scanner motor 26.

Although not shown, the motor driver 27 has circuits for protecting thescanner motor 26 against failure. These circuits include an overcurrentprotection circuit and an overheat protection circuit. If the scannermotor 26 is found faulty, the motor driver 27 sends to the faultdetection block 22 a driver error signal indicating the motor failure.The signal causes the optical apparatus or laser display apparatus tohalt its operation, illustratively shutting down the laser beamemission.

Information sent from the angle sensor 21 about the angle of the scannermotor 26 is forwarded in analog signal form to the motor driver 27.Alternatively, the information may be sent as a digital signal to thescanner motor 26.

The fault detection block 22 receives information about scanneroperation status such as instruction signals, angle information, anddrive current information illustratively from the motor driver 27. Onthe basis of the received information, the fault detection block 22sends to the overall control block 25 a signal such as a status signalindicating whether the scanner is operating normally or whether themotor is in a deteriorated state. The fault detection block 22 also hasthe ability to acquire data when the scanner is in normal operation andthe ability to compare normal data with the actually acquired data so asto detect any fault that may have developed.

The three major signals input to the fault detection block 22 aredescribed below.

(1) Drive Current Information

Driven generally by electric currents, motors including the scannermotor 26 produce a fault current in the event of a faulty operation. Thecurrent for driving the motor increases if a motor component fails andcauses greater friction. Detection of the drive current information thuscontributes to detecting a failure or fault of the scanner system. Upondetection of a failed state, a signal is sent to the overall controlblock 25 which in turn issues a stop command or an alert as needed.

(2) Instruction Signal Information

Although not shown, the overall control block 25 has an instructionsignal generation circuit and its related components including signallines. Any one of them may develop faults such as a disconnection orshort-circuit. The failure can cause changes in the behavior of some ofthe other components such as the motor driver 27 in the scanningsafeguard system 15. In such a case, it would still be possible todetect the failure using the drive current information, but a faster,more accurate way of fault detection is desired. This is accomplishedillustratively by the overall control block 25 inputting an instructionsignal directly to the fault detection block 22.

(3) Angle (or Speed) Signal Information

During laser beam projection, the angle and scanning speed of thescanner motor are the most important factors in maintaining a suitablydistributed state of laser beam energy. The angle information obtainedby the angle sensor 21 or the speed information based on the acquiredangle information is thus input to the fault detection block 22.

The fault detection block 22 uses the angle sensor 21 to sense therotation angle of the mirror in order to verify whether the scanner isoperating normally. That means the scanner is being monitored forfailure. The detection of any fault in the scanner is accomplishedillustratively by resorting to one or both of the following two methods:

-   -   (1) Detection of speed-related faults, such as signal        disconnection, power outage, mechanical failure, or acquisition        of error signal.    -   (2) Detection of cycle- and/or amplitude-related faults, such as        acquisition of error signal, servo circuit error, etc.

The detection of speed-related faults will now be described.

[Detection of Speed-Related Faults]

FIG. 6A shows a waveform representing angles of reciprocal rotation ofthe scanning mirror in the normally functioning scanner. FIG. 6B depictsa speed waveform obtained by differentiating the angles shown in FIG.6A. During normal operation, a low-speed state in which the laser beamis emitted and a high-speed state in which projection starting status isrestored are reciprocated.

FIG. 7 shows four waveforms in effect during normal operation with timedenoted by the horizontal axis. The waveforms comprise: an waveform(curve 61) representing the instruction signal sent to the motor driver27 of the scanner motor 26; a waveform (curve 62) representing mirrorangle information derived from the mirror being rotated according to theinstruction signal; a waveform (curve 63) representing differentialvalues derived from the angle information waveform 62 (i.e., waveform ofmirror rotation speed); and a waveform (curve 64) representing currentssupplied to the scanner motor 26.

In transitional states of decelerating to and accelerating from a steadyspeed, as plotted by the curve 63, there are two time periods Tslow_fand Tslow_r, each having a specific reference level (e.g., speed zero)interposed between two speed values Vth_L and Vth_H. Each of the timeperiods Tslow_f and Tslow_r remains constant as long as the rotatingmirror is normally reciprocating, the periods being repeated at fixedintervals.

A scanner failure will change the speed pattern. The failure leads tochanges in the time periods Tslow_f and Tslow_r or in their timing ofappearance. Sensing such changes makes it possible to detect a scannersystem fault. Illustratively, if the scanner motor breaks down andstops, the speed drops to zero. In that case, the time periods Tslow_fand Tslow_r are inordinately prolonged, or they appear in an abnormallytimed manner. Detection of these changes allows the scanner failure tobe recognized.

FIGS. 8A and BB graphically depict relations between angles and speedsin case of a failure. In this example, the point of fault occurrence isrepresented by Te. Before Te, regular angle changes are seen takingplace. After Te, no changes are observed in angle or speed. That canonly mean that the scanner is stopped.

The foregoing was a description of how the failure indicative of astopped scanner is detected by a speed detection setup based on theangles sensed by the angle sensor. In addition to the failureattributable to the scanner stoppage, a fault caused by deviations fromthe tolerable speed range can also be detected by the laser displayapparatus according to this invention.

In the latter case, a check is made to determine whether the mirrordriving mechanism is operating normally on the basis of a plurality offactors: the speed values Vth_L and Vth_H, the time periods Tslow_f andTslow_r, and speed changing cycles derived from these factors. Morespecifically, the two speed values Vth_L and Vth_H are first detectedand compared with predetermined settings. The results of the comparisonare used to find the time periods Tslow_f and Tslow_r. In turn, thesevalues are used to determine speed changing cycles. The obtained cyclesare compared with predetermined settings. The results of the comparisonsare finalized through AND operations.

FIG. 9 is a schematic block diagram of a typical fault detection blockaccording to the invention. The fault detection block of this exampleincludes: a differentiator 81 that translates angle information intospeed information; a memory 82 that holds the speed threshold valuesVth_L and Vth_H; and a comparator 83 for comparing the speed thresholdvalues Vth_L and Vth_H retrieved from the memory 82 with the speedinformation coming from the differentiator 81.

The fault detection block further includes: a memory 90 that retains thetime periods Tslow_f and Tslow_r, and decelerating and acceleratingperiod values; counters 84 and 85 for keeping count; comparators 86through 89 for comparing the results of the counting with the timeperiods Tslow_f and Tslow_r and the cycle values retrieved from thememory 90; and an AND circuit 91 which, by AND'ing the input results,determines whether the scanner is normal (represented by a 1) or faulty(represented by a 0). In this example, reference numeral 92 denotes atiming control block for controlling the drive timings of the counters84 and 85 and of the comparators 86 through 89.

The detection of cycle- and amplitude-related faults will now bedescribed.

[Detection of Cycle/Amplitude-Related Faults]

FIG. 10A shows a waveform representing angle information output by thescanning mirror. Levels Hth1 and Lth2 denote two over-scanning levels,one being a higher-than-normal level, the other being alower-than-normal level. Levels Hth2 and Hth1 are normal scanning levelsthat are crossed during normal operation and are for use in detecting acycle fault or an under-scanning fault.

That is, the levels Hth1 and Lth2 are not crossed during normaloperation. If the two levels are found crossed, then an amplitude fault(over-scanning) is recognized. Whether or not the scanning cycle isnormal is determined by monitoring the timings of the levels Hth2 andLth1 getting crossed. If these two levels are not crossed, both a cyclefault and an amplitude fault (under-scanning) are recognized.

FIG. 10B shows a signal waveform representing the levels Hth1, Hth2,Lth1 and Lth2 in effect when the angle information output is normal.That is, FIG. 10B illustrates status in which the angle informationoutput does not exceed the levels Hth1 and Lth2, i.e., where thedetected output is zero. Waveforms 93 and 94 are output waveformsobtained when the angle information output crosses the levels Hth2 andLth1. In FIG. 10B, upward and downward arrows indicate where thescanning cycle is detected. The upward arrows indicate points at whichthe cycle is detected while the mirror is scanning with the laser beam,and the downward arrows represent points at which the cycle is detectedwhile no effective scanning is being made (i.e., return period).

FIG. 11 is a schematic block diagram of the fault detection block fordetecting cycle- and amplitude-related faults. As illustrated, the faultdetection block includes: a memory 101 that holds reference dataapplicable to normal operation, and threshold values such as the levelsHth1, Hth2, Lth1 and Lth2; a memory 102 that retains normal operationcycles; comparators 103, 104, 105 and 106 for comparing the angleinformation measured by the angle sensor with the levels Hth1, Hth2,Lth1 and Lth2 supplied from the memory 101; counters 107 and 108 forcounting the results of comparison from the comparator 104; counters 109and 110 for counting the results of comparison from the comparator 105;comparators 111, 112, 113 and 114 for comparing the results of countingfrom the counters 107 through 110 with cycle signals retrieved from thememory 102; and an AND circuit 115 which, by AND'ing the input results,determines whether there exists any fault. The fault detection blockfurther comprises a timing control block 116 that synchronizes thecounters 107 and 108 and the comparators 111 and 112, and a timingcontrol block 117 for synchronizing the counters 109 and 110 as well asthe comparators 113 and 114.

The comparators 103 and 106 compare the angle information with thereference data and threshold signals (i.e., level signals Hth1 and Lth2)acquired from the memory 101. In this case, the comparators 103 and 106act to detect an exceeded level only if the angle information is input,i.e., if a signal crossing the level Hth1 or Lth2 is introduced. Theresult of the comparison is forwarded to the AND circuit 115.

The comparators 104 and 105 compare the angle information with the levelsignals Hth2 and Lth1 from the memory 101. The results of thecomparisons are fed to the counters 107, 108, 109 and 110. The counters107 and 109 count scanning cycle detection signals on the curves 93 and94 (points of detection indicated by upward arrows) in FIG. 10B, whilethe counters 108 and 110 count cycle detection signals on the curves 93and 94 (indicated by downward arrows). The timing control blocks 116 and117 make a changeover between the counters 107 and 108 on the one handand the counters 109 and 110 on the other hand.

The output from the counters 107 through 110 is supplied to thecomparators 111 through 114 respectively. These comparators compare whatis received with the cycle signals from the memory 102. From each of thecomparators 111 through 114, the AND circuit 115 receives a signalindicating whether the scanning is sensed as normal. In this case, too,the timing control blocks 116 and 117 make a changeover between thecomparators 111 and 112 on the one hand and the comparators 113 and 114on the other hand, while synchronizing the counters 107 through 110 andthe comparators 111 through 114. The AND circuit 115 ultimatelydetermines whether the scanner is functioning normally.

Described below with reference to FIGS. 12A, 12B, 13A and 13B is atypical setup for comparing the reference data and threshold valuesretrieved from memory with angle information, i.e., actually measureddata. In this example, differences are acquired between the referencedata from memory (indicated by straight line 201) and the measured data(curve 202) as shown in FIG. 12A. The differences thus obtainedconstitute difference data represented by a curve 203 in FIG. 12B. Thedifference data are compared with threshold values such as Th1 and Th2.The result of the comparison is examined so as to determine whether thescanner motor functions normally.

In the comparing setup above, a time period ΔT elapses from the time afault occurs until the fault is detected. If the threshold values Th1and Th2 are made appreciably large in the positive and the negativedirections respectively, as shown in FIG. 13A, then a fault detectiontime period ΔTa, i.e., the difference in time between a time T1 at whicha fault occurs and a time T2 at which the fault is detected, iscorrespondingly prolonged. On the other hand, if the threshold valuesTh1 and Th2 are made smaller in the positive and the negative directionsrespectively, as depicted in FIGS. 13B, then a fault detection timeperiod ΔTb, i.e., the difference in time between a time T3 at which afault occurs and a time T4 at which the fault is detected is shortenedaccordingly.

Where the fault detection time period ΔT is made inordinately short, thecomparing setup tends to detect even small deviations in the differencedata as faults. This can be a source of annoying stoppages. The faultdetection time period ΔT should thus be long enough to keep theinventive optical apparatus and laser display apparatus from gettingdisabled needlessly and small enough to afford an appropriately shortdetection span. As long as these requirements are met, desired thresholdvalues are allowed to be set on the optical apparatus and laser displayapparatus of this invention in keeping with their specific purposes.

The foregoing was a description of the angle information comparing setupaccording to the invention. Similar comparing setups are utilized by thefault detection blocks of the inventive optical apparatus for comparisonwith other types of information.

Described below with reference to FIGS. 14, 15 and 16 is how the faultdetection block typically acquires reference data and threshold values.In the optical apparatus and laser display apparatus according to theinvention, each fault detection block acquires reference data andthreshold values, and each comparison block compares the acquired datawith measured data. How these blocks work will now be described withreference to FIG. 14.

The comparing setup of FIG. 14 comprises: a data correction block 205made up of a CPU (central processing unit); a reference data acquisitionand data comparison block 206 for acquiring the reference data aboutdrive currents and comparing the acquired reference data with measureddata; a reference data acquisition and data comparison block 207 foracquiring the reference data about instruction signals and comparing theacquired reference data with measured data; a differentiation circuit208 that translates angle information into speed information; areference data acquisition and data comparison block 209 for acquiringthe reference data about the speed information coming from the circuit208 and comparing the acquired reference data with measured data; atiming control block 210 for controlling the blocks in accordance with aframe synchronizing signal; an AND circuit 211 which receivestemperature information from the CPU and AND's the input for feedbackcontrol purposes; and an optional block 212 that compares a projectionmode signal with an enable signal. The AND circuit 211 outputs a shieldcontrol signal based on the AND operation of the input from the blocks206, 207 and 209 as well as the input from the optional block 212 ifnecessary.

Described below with reference to FIG. 15 is a first example in whichthe fault detection block acquires reference data and threshold values.The first example applies illustratively upon shipment of the inventiveapparatus from the factory following manufacture. This example comprisesa data sampling circuit 221, a comparator 222, a memory 223, a filtercircuit 224, a memory 225, timing control blocks 226, 227 and 228; and adata correction block 229 typically formed by a CPU.

Upon shipment from the factory, the data sampling circuit 221 undercontrol of the timing control block 227 forwards reference data to thememory 225 through the filter circuit 224 for noise removal. Thereference data thus forwarded are placed into the memory 225.

When the apparatus is first used following shipment from the factory,the comparator 222 compares measured data from the data sampling circuit221 with the reference data placed in the memory 225 as well as with,say, threshold value data Th1 and Th2 in the memory 223. Uponcomparison, the detection block as a whole is controlled by the timingcontrol block 226. The data sampling circuit 221 is controlled by thetiming control block 227 and the comparator 222 by the timing controlblock 228. In this case, the reference data held in memory may becorrected for temperature by the data correction block 229 typicallymade of a CPU.

Described below with reference to FIG. 16 is a second example in whichthe fault detection block acquires reference data and threshold values.The second example applies illustratively where the user who purchasedthe inventive apparatus updates reference data as needed, or installs amemory that contains standard data serving as standards with respect toreference data, and a comparator for comparing the reference data withthe standard data in the memory.

Of the reference numerals in FIG. 16, those already used in FIG. 15designate like or corresponding parts, and their descriptions areomitted where redundant. Specifically, the components 221 through 229shown in FIG. 15 are supplemented in FIG. 16 by the following parts: amemory 232 holding standard data serving as standards with regard to thereference data in the memory 225; a comparator 230 for comparing thereference data in the memory 225 with the standard data in the memory232; and an AND circuit 231 that AND's the result from the comparator222 with the result from the comparator 230.

Upon shipment from the factory, the data sampling circuit 221 undercontrol of the timing control block 227 forwards the reference data tothe memory 225 through a filter for noise removal. The forwardedreference data are placed into the memory 225.

When the apparatus is first used following shipment from the factory,the comparator 222 compares the measured data from the data samplingcircuit 221 with the previously stored reference data in the memory 225as well as with, say, the threshold value data Th1 and Th2 placedseparately in the memory 223. In this case, the detection block as awhole is controlled by the timing control block 226. The data samplingcircuit 221 is controlled by the timing control block 227 and thecomparator 222 by the timing control block 228.

Later, the user who purchased the apparatus may have the data in thememory 225 updated by way of the filter circuit 224 as needed. If thereference data in the memory 225 are updated by the comparator 230 usingthe standard data in the memory 232, the comparison by the comparator230 of the standard data in the memory 232 with the reference datasubsequent to the comparison involving the data sampling circuit 221still allows the AND circuit 231 to provide overall relevant results. Inthis case, too, the reference data held in memory may be corrected fortemperature by the data correction block 229 typically made of a CPU.

FIG. 17 is a schematic block diagram of a determination signalacquisition block which acquires a determination signal based on theoutput from the fault detection blocks detecting faults by sensingspeeds, cycles and amplitudes as discussed above with reference to FIGS.9 and 11. This is an example in which a first and a second faultdetermination block are used to make doubly sure that the ultimatedetermination is reliable.

AND circuits are included to make sure that the laser beam projection ispermitted only if the results from all fault detection blocks arenormal. If any one of the fault detection blocks gives a resultindicative of a fault, the AND circuits function to terminate the laserbeam projection.

In FIG. 17, reference numeral 120 denotes a speed fault detection blockmade up of comparison circuits admitting the angle information from thespeed fault detection block shown in FIG. 9. Reference numeral 121represents a cycle/amplitude fault detection block formed by comparisoncircuits admitting the angle information from the cycle/amplitude faultdetection block depicted in FIG. 11. Determination signals output by theblocks 120 and 121 are input to the first fault determination block 122and the second fault determination block 123. The fault determinationblock 122 is illustratively composed of a CPU running software, and thesecond fault determination block 123 is formed by hardware. This dualdetermination scheme constitutes a fail-safe system. That is, the twoblocks can handle events in terms of both hardware and software.

In this example, an output circuit arrangement has AND circuits 124 and125 as well as amplifier circuits 126 and 127. This arrangement AND's adriver error signal, a scanner driver instruction signal (i.e., enablesignal), and a scanner driver internal error determination signal (i.e.,error flag). The result of the AND operation is output as adetermination signal (a “1” for projection enabled; a “0” for projectiondisabled).

Where the determination signal is suitably employed, the laser beamprojection is stopped in case of a scanner motor driver fault. Thisarrangement, too, is a dual circuit setup that constitutes a fail-safesystem. The first and the second fault determination blocks output astatus signal each, allowing the overall control block 25 of FIG. 4 tograsp the current status of the apparatus.

In addition to the above-described method, various alternative faultdetection methods may be conceived and practiced. One such methodinvolves having data such as angles and speeds sampled continuously forcomparison with reference data so that if the difference between thesampled data and the reference data exceeds a predetermined thresholdlevel, a fault is recognized. Another alternative method involves havingthe drive current monitored for comparison with reference data or forthe determination of an overvoltage. Where the angle information and areference signal are sampled and compared continuously, the faultdetection time period is obtained by the formula (1/sampling cycle+α).This method thus ensures high-speed fault detection.

Where the above-described structure of the invention is in use, a laserscanner fault triggers a shutdown or a stoppage of the laser beamprojection directed outward. This prevents an excessively powerful laserbeam from being emitted externally or getting directed at spots outsidethe regulated area, so that possible harmful effects on human bodies areaverted.

The above-described structure is designed primarily to deal with faultsthat may occur inside the laser scanner during operation. In order toensure higher levels of safety, it is preferable to implement astructure equipped with a diagnosis function for examiningcharacteristics of the laser scanner so that prior to its operation, thelaser scanner may be checked for potential fault.

What follows is a description of the diagnosis function that isimplemented typically to operate on the basis of a constant voltage,frequency modulation, or amplitude modulation.

The diagnosis function operates first of all based on a constant voltageas follows: a constant angle instruction signal is given to the scannersystem. The angle indicated by the signal is compared with actuallymeasured angle information to see if the scanner and the angle sensorare operating normally. In this case, the fault detection block 22 andprojection control block 23 in FIG. 4 may be monitored by the overallcontrol block 25 using the instruction signal so as to verify theoperation status of the components involved.

The diagnosis function also operates based on frequency modulation asfollows: the frequency for operating the scanner is varied betweensuitably low and high levels encompassing the normal frequency range.During the frequency variation, the components involved are monitoredfor operation status so as to determine whether fault detection isnormally carried out.

The diagnosis function further operates based on amplitude modulation asfollows: the amplitude of the instruction signal is varied betweensuitably small and large amplitude ranges encompassing the normalamplitude. During the amplitude variation, the components involved aremonitored for operation status so as to determine whether faultdetection is normally performed.

In the manner described, the components are examined for their operationstatus by the diagnosis function.

The scanning safeguard system is implemented using the inventive setupsdescribed above. The projector system as a whole is controlled by theflow of steps described below with reference to FIG. 18.

The system is first started up. The activated system is self-tested,i.e., examined by the diagnosis function. If the diagnosis detectssomething irregular, the laser beam projection is stopped, an alarm istriggered if necessary, and an error handling routine is carried out. Ifthe diagnosis detects nothing irregular, the scanner is allowed to startoperating. The operating scanner is checked by the scanning safeguardsystem for anything faulty. If a fault is detected, the laser beamprojection is stopped, an alarm is triggered as needed, and the errorhandling routine is executed. If nothing irregular is detected by thescanning safeguard system, the laser beam projection is allowed tocontinue normally. During operation, the scanner is being monitored andthe measured data are being sent back to the scanning safeguard systemfor feedback control.

As described, the optical apparatus and laser display apparatusaccording to the invention have the scanning safeguard system comprisinga plurality of fault detection blocks. In case of a fault such as alaser scanner failure, the fault is detected and the laser beamprojection is halted accordingly. This scheme forestalls a locallyimmobilized laser projection resulting in a substantially excessive doseof laser beam emission per unit area, thus ensuring that the safetystandards for laser beam emission are always complied with.

Furthermore, the inventive optical apparatus and laser display apparatusaccelerate the speed of fault detection by reducing the fault detectiontime period ΔT as discussed in conjunction with FIG. 13. Because thisinvention proposes techniques of fault detection based primarily on thedetection of laser scanner angles, the invention applies not only topolygon mirrors but also to galvanometer mirror scanners that arechecked for failure reliably by the scanning safeguard system.

The invention thus provides higher levels of safety and other relatedbenefits for display apparatuses such as laser beam projectors. Inparticular, the projector can be operated to project images onto a largescreen at high levels of luminous intensity with enhanced safety.

As many apparently different embodiments of this invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

1. An optical apparatus having a scanner for scanning a predeterminedarea with a laser beam, said optical apparatus comprising: a lasersource; the scanner having a scanning mirror for causing a laser beamgenerated by said laser source to scan; an angle sensor for sensingangles of said scanning mirror of said scanner; a fault detection blockfor determining whether said scanning mirror operates safely andnormally based at least on angle information coming from said anglesensor; and a projection control block for controlling projection ofsaid laser beam based on fault detection information coming from saidfault detection block. 2-10. (canceled)